1. Field of the Invention
The present invention relates to a hydraulic actuator unit including a hydraulic actuator such as a hydraulic pump main body, variable displacement mechanism for changing a displacement of the hydraulic actuator, and an electric motor for actuating the variable displacement mechanism.
2. Related Art
With regard to a hydraulic actuator unit such as a hydraulic pump unit or an HST unit, which includes a hydraulic actuator such as a hydraulic pump main body and a variable displacement mechanism for changing a displacement of the hydraulic actuator, there has been proposed a configuration in which the variable displacement mechanism is actuated with use of an electric motor (for example, US Patent Application Publication No. 2006-0272495).
The conventional hydraulic actuator unit is useful in that operation force required for actuating the variable displacement mechanism could be reduced, since the electric motor actuates the variable displacement mechanism so as to change the displacement of the hydraulic actuator.
However, the hydraulic actuator unit disclosed in the US patent application publication has following problems.
The US patent application publication discloses the hydraulic actuator unit in the form of hydraulic pump unit.
Specifically, the hydraulic actuator unit includes a pump case, first and second pump shafts, first and second hydraulic pump main bodies, first and second variable displacement mechanisms, and a pair of electric motors. The first and second pump shafts are supported by the pump case in a rotatable manner around their respective axis lines in a state of being parallel to each other and being operatively connected to each other. The first and second hydraulic pump main bodies are accommodated in the pump case in a state of being supported by the first and second pump shafts in a relatively non-rotatable manner with respect thereto. The first and second variable displacement mechanisms change displacements of the first and second hydraulic pump main bodies, respectively. The pair of electric motors actuate the first and second displacement mechanisms, respectively.
The first pump shaft has first and second ends that are positioned on one side and the other side in its axis line direction, the first end being extended outward from the pump case to form an input end to be operatively connected to a driving power source. The second pump shaft has first and second ends that are positioned on the same side as the first and second ends of the first pump shaft with respect to the axis line direction, respectively, the second end being extended outward from the pump case to drive a cooling fan.
The first variable displacement mechanism includes a control shaft (hereinafter referred to as first control shaft) that is supported by the pump case in a rotatable manner around its axis line in a state where its first end is inserted into the pump case so as to be operatively connected to a corresponding variable swash plate and its second end is extended outward from the pump case.
The second variable displacement mechanism includes a control shaft (hereinafter referred to as second control shaft) that is supported by the pump case in a rotatable manner around its axis line and in parallel with the first control shaft in a state where its first and second ends are faced in the same direction as the first and second ends of the first control shaft. The first end is operatively connected to a corresponding swash plate, and the second end is extended outward from the pump case.
One (hereinafter referred to as first electric motor) of the pair of electric motors is mounted to the pump case via an electric motor cover (hereinafter referred to as first electric motor cover) so as to rotate the second end of the first control shaft around the axis line, while the other one (hereinafter referred to as second electric motor) of the pair of electric motors is mounted to the pump case via an electric motor cover (hereinafter referred to as second electric motor cover) so as to rotate the second end of the second control shaft around the axis line.
Specifically, the first electric motor cover supports the first electric motor so that an electric motor main body of the first electric motor is positioned on an opposite side to the first end of the first pump shaft with respect to a first virtual surface that passes through axis lines of the first and second control shafts.
On the other hand, the second electric motor cover is symmetrical to the first electric motor cover with respect to a second virtual plane that is orthogonal to the first virtual plane and passes through a center between the first and second control shafts. Specifically, the second electric motor cover supports the second electric motor so that an electric motor main body of the second electric motor is positioned on the same side as the second end of the second pump shaft with respect to the first virtual plane.
In the conventional hydraulic actuator unit with the configuration, the cooling fan has to be away from the pump case in such a manner as that the cooling fan, which is mounted on the second end of the second pump shaft, is not interfered with the second electric motor, resulting in an enlargement of the hydraulic actuator unit as a whole.
Moreover, as explained above, the first and second electric motor covers are symmetrical to each other with respect to the second virtual plane. Specifically, in the conventional hydraulic actuator unit, the first electric motor cover is exclusively used for mounting the first electric motor and the second electric motor cover is exclusively used for mounting the second electric motor, rather than the first and second electric motor covers have the same configuration to each other.
Accordingly, in the conventional hydraulic actuator unit, it is likely to cause a mistake in assembling work of the first and second electric motors to the pump case, resulting in worsened assembling workability of the first and second electric motors while involving complicated inventory management of the first and second electric motor covers.
Furthermore, the conventional hydraulic actuator unit does not take into account cases where the variable displacement mechanism needs to be manually operated upon breakdown or mode change of the electric motor. Therefore, the conventional hydraulic actuator unit has difficulties in changing modes between the electric mode of actuating the variable displacement mechanism with use of the electric motor and the manual mode of manually actuating the variable displacement mechanism.